Thanks to Graeme, ZL2APV, quisk now changes both channels of a control when using mixer_settings. He reports that setting boolean values does not work, but it works on my machine. More testing is needed.
The new config file dictionary bandTransverterOffset gives the offset in Hertz for bands that are used with a transverter; for example 144000000 - 28000000 for a two meter transverter. This currently works for HiQSDR, SoftRock and SdrIQ. I also changed the graph X axis code so gigahertz frequency labels are not too wide.